Scientists looking at combating mosquito epidemic

SINGAPORE - The aim: Stop the dengue surge. The method: Suppress the Aedes mosquito population in Singapore.

The strategy: Release sterile male Aedes mosquitoes infected with the Wolbachia bacterium.

The sterile mosquitoes' mating will cause a drop in the population, while the bacterium prevents the growth of the dengue virus.

As the number of dengue cases surged past 10,000 this year, scientists at the National Environment Agency's (NEA) Environmental Health Institute (EHI) are looking at doing just that.

Working together with biotech company Oxitec in Britain and Monash University in Australia, they conduct laboratory studies to test the potential and risks in the Singapore context.

Oxitec uses radiation to genetically sterilise male Aedes mosquitoes and release them to mate with females in the wild. Any offspring as a result of the mating will not survive to adulthood.

The group from Monash University infects the Aedes with the Wolbachia bacterium - which not only shortens the life-span of the mosquito but make it resistant to infection by the dengue and chikungunya viruses - before releasing them into the wild.

An NEA spokesman told The New Paper that the agency is looking at an alternative approach - using only Wolbachia-infected males, which behave like the genetically sterilised ones - to suppress the mosquito population.

Effectiveness unknown

Oxitec had conducted field trials in Brazil, the Cayman Islands and Malaysia, and while preliminary results had shown some level of success in population suppression, its impact on dengue transmission in still unknown.

The Australian group using Wolbachia has also carried out field trials in Australia, and has just begun releases in Vietnam, Indonesia and Brazil.

The impact of their release on dengue has also not been demonstrated.

The majority of the current dengue clusters continue to be in the eastern part of Singapore but there is an increasing number of clusters in the western and northern parts.

The dengue season is expected to last till September.

And despite the dengue clusters this year being bigger than usual and active for a longer period, scientists at EHI still want to be cautious with the novel techniques.

"Our unique circumstances - highly urbanised environment, comparatively low levels of adult mosquitoes, low herd immunity to dengue - require us to make careful evaluation of these novel approaches to ensure they can achieve a demonstrable impact on dengue without negatively impacting our natural ecology," said the NEA spokesman.

The agency continues to endorse source reduction and the removal of potential breeding habitats through environmental management.

And in areas that cannot be reached, NEA has been using Bti, a bacteria toxin that kills mosquito larvae.

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